An islated rat brain preparation will be perfused with different concentrations of drugs (methadone, morphine, chlorpromazine and others). The effects of the drugs on the brain will be evaluated by chemical analysis of the brain tissue for energy stores (creatinephosphate, ATP, ADP and AMP), metabolites of glucose (glycolytic intermediates) and redox status (lactate/ pyruvate). The effects of the drugs on the electrical activity will be recorded from stereotaxically placed electrodes in discrete areas of the brain of intact rats and in the isolated perfused brain. The effects of the drugs on the biogenic amines will be evaluated by chemical analysis and by histochemical methods.